Method for encasing electrical apparatus



Aug. 2, 1966 N. CHESSIN ETAL METHOD FOR ENGASING ELECTRICAL APPARATUS Original Filed Sept. 11, 1961 4 Sheets-Sheet 1 [flue/750229. Newton (/zesszn, 1 Prank/#7 E v v amer/n39.

Aug. 2, 1966 cHEssm T 3,264,395

METHOD FOR ENCASING ELECTRICAL APPARATUS Original Filed Sept. 11, 1961 4 Sheets-Sheet 2 fm/ent'orzs Nan/6'0)? Chess/'17, Fran/2W 95 0 0811;

Aug. 2, 1966 N. CHESSIN ETAL METHOD FOR ENCASING ELECTRICAL APPARATUS Original Filed Sept. 11. 1961 4 Sheets-Sheet I5 Aug. 2, 1966 N. CHESSIN ETAL METHOD FOR ENCASING ELECTRICAL APPARATUS 4 Sheets-Sheet 4 Original Filed Sept. 11. 1961 United States Patent 3,264,395 METHOD .FOR ENCASING ELECTRICAL APPARATUS Newton Chessin, Maitland, Fla, and Franklin P. Eppert, Danville, 11]., assignors to General Electric Company, a corporation of New York Original application Sept. 11, 1961, Ser. No. 137,339, now Patent No. 3,219,884, dated Nov. 3, 1965. Divided and this application June 22, 1965, Ser. No. 466,918

' 2 Claims. (Cl. 264-272) This application is a divisional application of our copending application filed September 11, 1961 Serial No. 137,339 now United States Patent No. 3,219,884, granted on November 3, 1965.

This invention relates to encased electrical apparatus and to a method for encasing such apparatus with insulating-material. More particularly, it relates to a method for encasing such ballast apparatus in a casing of insulating material, such as a synthetic resin.

Heretofore, it has been a common practice to encase electrical apparatus such as transformers, inductors, and electrical coils with various insulating compounds by casting an insulating material about the electrical device. It has also been a common practice to place the components of an electrical device, such as a ballast apparatus, in a metallic case or cannister and then to fill the case with an insulating potting material which generally includes asphaltic compounds as a constituent thereof.

The potting materials generally used in ballast applications require a protective covering, such as a metallic case, since the potting materials are relatively plastic and hygroscopic. In applications where a ballast apparatus 1s exposed to a wide range of conditions, such as humid and corrosive atmospheres and relatively high and low temperature environments as may be encountered in various extremes of the weather, the metallic case of the ballast apparatus frequently corrodes. The destruction of the case by corrosive action may cause the potting material to fiow from the case under high temperature conditions and may result in excessive amounts of moisture absorption by the apparatus. Upon either event such conditions may eventually lead to a premature electrical failure of the ballast apparatus.

In the past, the components of ballast apparatus for operating and starting gaseous discharge lamps, such as fluorescent lamps, have not been successfully encased in a cast or molded resinous casing without need for a metallic case to contain the resin. One of the principal difiiculties encountered was cracking of the casing. As the ballast apparatus is operated under a wide range of environmental conditions, the casing is subjected to dimensional and dynamic effects. These effects are aggravated in a ballast apparatus because it includes a plurality of components, such as a liquid dielectric filled capacitor and shell type of high reactance transformer. Cracking is, of course, objectionable since the cracks provide paths for the entrance of moisture into the electrical device and consequently may cause an electrical failure of the device. There is, therefore, a need for a ballast apparatus which is completely encased in an insulating resinous material that does not require a metallic protective case. Further, there is a need for a method for encasing such apparatus wherein a plurality of electrical components can be encased in a case or molded insulating material which is not susceptible to cracking and is thereby impervious to moisture.

It is an object of our invention to provide a new and improved method for encasing an electrical apparatus containing a plurality of components in a moisture impervious vasing of resinous insulating material.

In accordance with one form of our invention ballast apparatus was encased by a method including the steps of fixedly attaching one end of a ballast capacitor to one end of a magnetic core and coil assembly to form an elongate assembly, connecting the capacitor and magnetic core and coil assembly in operative relationship with each other and with external leads, arranging the leads brought out for external connection so that a riser is formed for the resin to be cast within the interior of the jacket and wrapping reinforcing cloth around the capacitor and the magnetic core and coil assembly. The wrapped elongate assembly is then placed in a mold, liquid resin is poured in the mold so that the interior of the jacket is filled and so that the exterior thereof is completely encased, and the resin is cured to form a solid infusible mass.

In another aspect of the invention we have provided a nipple which is rigidly attached to the outer end of the capacitor and may be insulated therefrom if the nipple is made of metallic material. Also, a conical spacer made of the resinous insulating material is attached by suitable adhesive means to the outer end of the magnetic core and coil assembly. The nipple and the conical spacer serve to position the wrapped assembly during the casting operation. In addition, the nipple serves as a connector for a conduit box and as a conduit for the external leads.

The subject matter which We regard as our invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be better understood by referring to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an exploded view in perspective of the capacitor assembly;

FIGURE 2 is a perspective view illustrating the assembly of the magnetic core and coil assemblies, one of the magnetic core and coil assemblies being partially broken away to illustrate how the conical spacer is attached to one end thereof;

FIGURE 3 is a perspective view of the elongate as sembly of the magnetic core and coil assemblies and capacitor;

FIGURE 4 is a perspective view of the elongate assembly corresponding to the view shown in FIGURE 3 wherein portions of the jackets are cut away to illustrate how the leads are brought out and how a riser is formed for the fiow of resin to the interior of the jacket;

FIGURE 5 is a partially sectionalized view showing how the wrapped elongate assembly is positioned within a mold and how the liquid resin is poured therein;

FIGURE 6 is a perspective view of the centering ring;

FIGURE 7 is a fragmentary view illustrating the mold completely filled;

FIGURE 8 is a schematic illustration of molds placed in an oven to cure the resin into a solid infusible mass;

FIGURE 9 is a perspective view of an encased ballast apparatus in accordance with the invention; and

FIGURE 10 is a view of cutaway portion of the encased ballast shown in FIGURE 9.

Referring more specifically now to FIGURE 1, it will be seen that a pair of spacers 10, 11, an insulating strip 12 and a nipple 13 are provided for assembly on a capacitor 14. The insulating strip 12 serves to insulate the metallic nipple 13 from the capacitor 14 and was attached to one end of the capacitor 14 by means of a suitable adhesive. The nipple 13 was then attached to the insulating strip 12. At the other end of the capacitor 14, the spacers 10, 11, which in the illustrated embodiment of the invention were made of wood or plastic, were attached thereto by the adhesive. The spacers 10, 11 control the spacing between the end of the magnetic core to which capacitor 14 was attached so that electrical connections may be made thereto and served to align the capacitor 14 along a longitudinal axis 15. Since the nipple 14 used in the illustrated embodiment of the invention was fabricated of aluminum and since the nipple 14 is gener-.

ally connected to a grounded junction box, it was necof insulating material or where it is desirable to connect the capacitor case to ground, .the insulating strip 12 may be eliminated. V

In the exemplification of the invention, the nipple 13 was centered at the end of the capacitor 14 since, as will hereinafter be more fully explained, the nipple 13 also serves to align the entire ballast apparatus; during'the casting operation along the longitudinal axis 15. The opening 9 formed atone end of the nipple 13was provided so that the external leads can be brought out,from;the ballast apparatus.

In FIGURE 2 there is shown a pair of magnetic core and coil assemblies 16, 17,one of which is broken away.

The magnetic core and coil assemblies 16, 17 are of-con-.

ventional construction having shell-type cores 18, 19

formed of magnetic laminations held together at each end by clamping elements 20, 21 and 22, 23, respectively. A

pair of coils 24, 25 are mounted on the winding leg of magnetic core 18.and a similar pair of coils 26, 27 are mounted on the winding leg of magnetic core 19.

- As shown in the broken-away. portionof the magnetic core 19 illustrated in FIGURE 2, a conical spacer 28 was bonded to clamping element 23 by'an epoxy adhesive and was positioned along the longitudinal axis 15. The.

spacer 28 serves a dual function. First of all, itprovides a predetermined spacing of one end of the magnetic core and coil assembly 17 from the bottom of the mold and thereby determines the thickness of the resinous insulating material at the'end thereof. Secondly, the apex of the conical spacer serves as a centering point for the apparatus when placed in the mold, as will hereinafter be more fully explained. Further, it was found that by placing the apex as shown, it is barely discernible on the sur face after the casting operation is completed and no objectionable surface defect results from the use of the conical spacer 28.

The conical spacer 28 was preferably cast from the same resinous material used as the casting material for the casing of the ballast apparatus. Other materialwith a similar. coefficient of thermal expansion may be used. It was found that where the spacer 28 is of the same material, it readily adheres to the casing after it is cast and any relative movement between the surfaces of the spacer 28' and the casing during temperature cycling was minimized. A conical configuration, or a thin rod,'is preferred since it minimizes cracking caused by stresses resulting from the curing of the resinous material adjacent to'the spacer.

It will be appreciated that although the ballast apparatus constructed in accordance with the invention had two magnetic core and coil assemblies 16, 17, the invention is equally applicable to more conventional types of ballast apparatus wherein a single magnetic core and coil assembly is used. Where two magnetic core and coil assemblies 16, 17 are employed, the ends thereof or the clamping elements 21, 22, as shown in FIGURE-2, are fixedly attached so that the two magnetic core and coil assemblies 16, 17 are aligned along the longitudinal axis 15. Spacers 31,32 may be employed or, if desired, a sufliclent amount of adhesive may be placed between the clamping elements 21, 22, to attach the two magnetic core and coil assemblies 16, 17 in fixed and spaced relationship.

Turning now to FIGURES, it willbe seen, that the two magnetic core and coil assemblies 16, 17 are shown in a suitable jig 30 illustrated in dashed outhne. The ig 30 held the capacitor 14 land the magnetic core and coil assemblies 16, 17 in longitudinal alignment while" the gluing operation was carriedout to assemble them in fixed and spaced relationship. In the exemplification of the invention an epoxy resin glue was used which cured Itt at roomtemperature andhad the: followingv formulation, the parts set forth below being by weight:

Epon 828 100 Eparts. Ethylene :oxideadiethylene triamine adduct with 30-40% Bisphenol A 20-25 parts per hundredof resin.

Asbestos 30-50 parts per hundredof resin.

The epoxy resin knowncommercially asEpon 828jis fully described in application Serial Number 71,146, filed on November 23,1960, in the name of Marvin A. Peterson and assigned to' the same; assignee as the" present invention, which applicationis incorporated herein by reference.-

After the gluing operation was completed, the capacitor A 14, ;the magnetic core and coil assemblies 16, 171,; and ex-' ternal leads, 35, 3 6,37,38,69, 40, 41, 42 .are connected t in operative circuit relationship, as shown in FIGURE .4.

Priorto wrapping, the-leads may be held in positionby" masking tape 43.. It will be noted that atthe left end, as seen H1 FIGURE 4, a riser 44 is formed by grouping; the.

external leads 35,; 36, 37 ,l38, 539, 40; 41, 42 which serve I as the sides thereof. The .bottom side. of the. riser44 is;-

provided by the-capacitor 14 and. the top side thereof,;by

a paper, part 45 held in 'positionby masking tape 43.1 If? desired, a tube of paper or other suitable materialmay be used to form the riser.

Masking tape43 or other suitable means may 'be used in order to hold'the leads in position and facilitate han-- the nipple 14 andpositioned to form a riser 441 as. here-.. inbefore described, the step of'wrapping the assembly is;

carried out. Initially, the reinforcing cloth wrapping 146 A was folded across the bottom clamping element 23. which hasthe conical spacer 28 attached thereto. The conical spacer 28 was allowed to penetrate through the end piece of the cloth wrapping 46.- The cloth wrapping 46- was then continuously wound about the core .and coil assemblies 16; 17 and. the capacitor v14 toform a jacket.47.- Preferably, thecloth wrapping 46 was wound so that it was at least half lapped .or ineffect provided .at least two layers of clothwrapping aboutthe assembly. In the ex-v emplification of'the invention the cloth wrapping 46 was lapped so that three layers were provided. The left end.

ofthe jacket 47, as seen in FIGURE4, was left open, singe the resinous insulating material is poured'from this en The cloth wrapping 46 used in the exemplificatiomof V the inventionwas afiber glass material having a plain; weave pattern,"a weight of 8.71 ounces per square yard,

18 threads. per inch warp and. 17 threads per. inch fill.

rounded surfaces thereby minimizing stress effects. The

insulating material within the interior of the jacket is, however, sub ected to the stresses occurring at the sharp edges. Jacket 47 prevents any cracking which may occur 1n insulating material within the interior of the jacket 47 from propagating to the body. of insulating material to be cast around the exterior of the-jacket 47. Further, it was. found that the jacket 47 also minimizes the effects of externally appliedimpacts.

When the wrapping operation was completed, the wrapped assembly was then placed in a mold 48 as shown in FIGURE 5. The mold 48 includes a base member 49, a mold tube 50, a release film 51, a centering ring 52, and a clamp 54, as shown in FIGURE 5. A perspective view of the centering ring 52 is shown in FIGURE 6. It Will be seen that the conical spacer 28 extending from the end of the wrapped assembly was positioned in a locating hole provided at the center of the \base member 49. In this manner the lower end of the wrapped assembly is accurately positioned within the mold 48, so that the thickness of the resinous material 55 to be cast around the assembly can be efiectively controlled. At the upper end of the mold 48, the assembly is centered along the longitudinal axis 15 by means of the centering ring 52, which centers nipple 13 attached to the capacitor. The clamp 54 holds the mold tube 50 and film 51 tightly against the base member 49 in order to prevent leakage of the liquid resinous material 54 from the mold 48.

In the illustrative embodiment of the invention, the paper mold tube 50 was lined with a liner 51 made of a polyester film such as polyethylene terephthalate. The liner 51 was used to prevent adhesion of the resin to the paper tube 50. Further, the use of the liner 51 resulted in a smooth, glossy surface when the resinous material was cured.

The mold 48 was filled from the top with a polymerizable resin composition having suitable properties for use as an encapsulating material. In the exemplification of the invention, polymerizable mixtures of unsaturated polyesters and epoxy resin described and claimed in the aforementioned application Serial No. 71,146 were used. The resin mixtures disclosed therein were readily pourable liquids. The liquidpolymerizable resin mixture was poured into the mold by means of two nozzles 57, 58 disposed over the openings in the centering ring 52 so that the liquid resin fills the interior of the jacket 47 and so that the outside of the jacket 47 is completely filled to form a fluid impervious casing when cured. As shown in FIGURES 7 and 9, it will be seen that since the mold is cylindrical in configuration, the apparatus is encased in a cylindrical body of resinous material 55. The apparatus encased in the cylindrical casing of resinous material 55 can be readily mounted in any position by reason of a pair of support brackets 61, 62. It will be understood that the mold 48 may be formed to other configurations, if desired. For example, in order to reduce the amount of resinous material, it may be desirable to form the mold in a configuration that more closely conforms to the apparatus.

Since in the exemplifications of the invention, the polymerizable resin mixture used required the application of heat for curing, afiter the filling operation was completed, the filled mold 48 was passed through an oven 60 such as shown in FIGURE 8, and the curing of the res-in mixture was carried out at an elevated temperature. It will be appreciated that the step of heat curing may be eliminated where the polymerizable liquids used are curable at room temperatures.

Referring now to FIGURE 10, it will be noted that an inner body 64 and an outer body 65 are formed, the inner and outer bodies 64, 65 being separated by the woven glass jacket 47. The outer body 65 serves as the structural enclosure for the ballast apparatus. The inner body 64 of insulating material 55 and the woven glass jacket 47 take up the stresses resulting from movement of the magnetic core and coil assembly and the capacitor case resulting from temperature cycling and other causes. It was found that the woven glass jacket 47 eifectively prevents propagation of cracking that may occur in the inner body 64 to the outer body 65. Thus, in accordance with the invention, we have provided an improved method for encasing electrical apparatus having a plurality of components in a molded resinous casing without need for a protective metallic case to house the apparatus.

While the present invention has been. described with reference to particular embodiments and examples, it will be understood that modifications may be made as will be apparent to those skilled in the art. It is, therefore, intended by the appended claims to cover all such modifications that fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method for encasing an electrical apparatus having a capacitor and at least one magnetic core and coil assembly, said method comprising the steps of: rigidly attaching one end of said capacitor to one end of the magnetic core to form an elongate assembly, connecting said capacitor and magnetic core and coil assembly in operative circuit relationship with external leads, said external leads being brought out at one end thereof to form a riser for the passage of liquid resin, wrapping cloth of reinforcing material around at least a portion of said leads, said capacitor and said core and coil assembly to form a jacket substantially circumscribing said apparatus, placing said wrapped and connected magnetic core and coil assembly and capacitor in a mold, pouring a liquid polymcrizable resin into said mold so that it fills the interior of said jacket and so that an outer body substantially encasing said apparatus is formed, and curing said resin to a solid infusible mass.

2. A method for substantially encasing a ballast apparatus having at least one magnetic core and coil assembly and a capacitor, with a castable insulating material, said method comprising the steps of: attaching a nipple to one end of the capacitor substantially centered about the longitudinal axis thereof, attaching the base of a conicalshaped spacer formed of the resinous insulating material to one end of the magnetic core assembly and substantially along the longitudinal axis thereof, joining the other end of the magnetic core and coil assembly with the other end of said capacitor in rigid and spaced relationship, connecting said capacitor and said core assembly in operative circuit relationship and in circuit with external leads, bringing out said external leads through said nipple, wrapping said entire assembly with a woven reinforcing cloth to form a jacket substantially enclosing said assembly, placing said jacketed assembly in a mold, said conical spacer centering one end thereof in the mold and said nipple centering the other end thereof in the mold, pouring liquid castable insulating resin into said mold so that the interior of said mold jacket is filled with resin and so that an outer body of insulating material is formed that substantially encases said apparatus, and curing said resin to form a solid infusible mass.

References Cited by the Examiner UNITED STATES PATENTS ROBERT F. WHITE,

L. S. SQUIRES, Assistant Examiner.

Primary Examiner. 

1. A METHOD FOR ENCASING AN ELECTRICAL APPARATUS HAVING A CAPACITOR AND AT LEAST ONE MAGNETIC CORE AND COIL ASSEMBLY, SAID METHOD COMPRISING THE STEPS OF: RIGIDLY ATTACHING ONE END OF SAID CAPACITOR TO ONE END OF THE MAGNETIC CORE TO FORM AN ELONGATE ASSEMBLY, CONNECTING SAID CAPACITOR AND MAGNETIC CORE AND COIL ASSEMBLY IN OPERATIVE CIRCUIT RELATIONSHIP WITH EXTERNAL LEADS, SAID EXTERNAL LEADS BEING BROUGHT OUT AT ONE END THEREOF TO FORM A RISER FOR THE PASSAGE OF LIQUID RESIN, WRAPPING CLOTH OF REINFORCING MATERIAL AROUND AT LEAST A PORTION OF SAID LEADS, SAID CAPACITOR AND SAID CORE AND COIL ASSEMBLY TO FORM A JACKET SUBSTANTIALLY CIRCUMSCRIBING SAID APPARATUS, PLACING SAID WRAPPED AND CONNECTED MAGNETIC CORE AND COIL ASSEMBLY AND CAPACITOR IN A MOLD, POURING A LIQUID POLYMERIZABLE RESIN INTO SAID MOLD SO THAT IT FILLS THE INTERIOR OF SAID JACKET AND SO THAT AN OUTER BODY SUBSTANTIALLY ENCASING SAID APPARATUS IS FORMED, AND CURING SAID RESIN TO A SOLID INFUSIBLE MASS. 